The most energetic particles in the universe have a message for us. The gigantic Pierre Auger Southern Observatory, still under construction in Argentina, is already trying to decipher it.

By Davide Castelvecchi

Toward the end of a ten-year experiment in 1991, postdoc Hungye Dai of the University of Utah was puzzling over some really unusual data. The experiment was Fly’s Eye, which pioneered a new method of studying ultra-high-energy cosmic rays by monitoring the faint flashes of ultraviolet light produced in the sky when the particles hit the upper atmosphere. Lead scientist Pierre Sokolsky recalls when Dai showed him the anomalous numbers. Sokolsky thought they were a fluke from the detector: “You know, you always expect to see stuff like that, and it’s usually just junk,” says Sokolsky. “So I told him to go away, and to look at it some more.